On performance improvement for 802.11-based multi-hop ad hoc wireless networks

Collision due to the hidden terminals in contention-based medium access control protocols is one of the main reasons of the poor end-to-end performance of wireless networks. In this paper, we present a novel approach for MAC protocol improvements for 802.11-based multi-hop ad-hoc wireless networks to reduce unnecessary collisions, resulting in performance enhancement. Our main idea is to reduce unnecessary collisions by introducing a new time interval, named CAI (Collision Avoidance Interval) for the node in the carrier sensing zone[6]. Specifically, in the context of 802.11, the four-way handshake is specified as a collision avoidance medium access protocol and the protocol behavior for the node in the carrier sensing zone is required to be modified when it senses a signal for CTS, such that the node defers transmitting a frame during CAI, unlike during EIFS in the 802.11 specification. We carry in-depth analysis of the protocol behavior and have conducted a comprehensive simulation to study the performance improvements. The simulation results show that the end-to-end performance is greatly increased and the number of dropped frames due to collision is significantly reduced as much as one half, and so is the throughput cost.